My trainer told me if you can make it through the first 3 weeks, you are WELL on your way. During this initial phase, your body struggles because you are weaning yourself off certain foods and chances are you are stepping up your training a lot. It is hard and your body is trying to adjust....but that difficulty also is a sign that things are changing and the program is working

After a few weeks, I think it's easier to continue. Cheating or quitting negates all that hard work you put in and makes it futile. I think, "If I eat this one thing, it trivializes all the times I said No to cheating and all the times I trained even though I was tired." I refuse to do that.
I also find that once you clear that hurdle of getting in decent shape (you lose the excess weight and shape up cardiovascularly) you have an easier time performing your training. Once the scales tip, everything is a bit easier! And once you see those changes you get so excited to keep the ball rolling. I am within a month of my first show this season and I love that every morning I see something new on my physique!
And what everyone else said is true...the thought of being on stage in nothing but a few inches of fabric is enough to keep me on the straight an narrow!!!!!
Stay strong girl and know you are not the only one toughing it out. Lots of us are getting ready to compete and we are doing the same things...and so is your competition
Good luck!